Common sex therapy is only for help with sexual problems but global ex therapy is for all kinds of help with mental problems such as anxiety,nervousness,loss of self esteem,and some times social phobia ect.
In places where prostitution is legal they can get a prostitute to help with sex if she goes through a small training course and health exam and they have people on staff that have been trained to give sex in this context.
The word global in global sex therapy means it is used for all types of mental health treatment and not just sexual.